Satellite radio operators are providing digital radio broadcast services covering the entire continental United States. These services offer over 120 channels, of which nearly 50 channels in a typical configuration provides music with the remaining stations offering news, sports, talk and data channels. Briefly, the service provided by XM Satellite Radio includes a satellite X-band uplink to two satellites which provide frequency translation to the S-band for re-transmission to radio receivers on earth within a coverage area. Radio frequency carriers from one of the satellites are also received by terrestrial repeaters. The content received at the repeaters is retransmitted at a different S-band carrier to the same radios that are within their respective coverage areas. These terrestrial repeaters facilitate reliable reception in geographic areas where LOS reception from the satellites is obscured by tall buildings, hills, tunnels and other obstructions. The signals transmitted by the satellites and the repeaters are received by SDARS receivers which can be located in automobiles, in handheld or in stationary units for home or office use. The SDARS receivers are designed to receive one or both of the satellite signals and the signals from the terrestrial repeaters and combine or select one of the signals as the receiver output.
Existing FM radio receivers or other customized FM radio receivers can be retrofitted to receive the satellite digital radio broadcast and enable one to listen to the programming via an unused FM frequency using an RF modulator. As shown in FIG. 1, an audio system 3 can include an FM modulator 5 that is connected to a head unit 6 (via an FM switch) and corresponding FM antenna 6 via a coaxial cable or transmission line 9 to enable a full frequency response. To receive the satellite digital audio radio transmission, the audio system 3 further requires a satellite antenna 4 and an antenna module 2 coupled to a satellite receiver 1 via another coaxial cable or transmission line 8. The required cabling in an automotive environment for such a set up as shown in FIG. 1 can be a little cumbersome and involve additional cost in terms additional wiring. Currently, satellite radios must either be permanently installed in vehicles or connected to a car stereo via the cassette deck. Permanent installation is costly and requires professional installation, which is unattractive to many consumers. Moreover, many vehicles do not have cassette decks. Thus, a need exists for a way to eliminate additional cabling when retrofitting or initially installing a radio system to receive a source signal such as a satellite digital audio radio signal or other digital source signal.
Furthermore, vehicles come in various configurations and various factory installed antenna arrangements. Since the Federal Communication Commission (FCC) requires that an FM modulated signal radiating a source signal must be below a predetermined power level, the effective arrangements for wirelessly re-broadcasting a source signal via an FM modulator are limited. There are currently no existing FM modulator arrangements that can effectively cover all the existing FM antenna arrangements for automobiles unless cumbersome cabling or wiring is used. For example, automobile FM receive antennas can be embedded in a front or rear windshield which can possibly receive a internally radiated FM modulated signal without cabling, but will likely fail to reach a common external FM receive antenna. If a externally radiated FM modulated signal is provided without cabling to a common external FM receive antenna, placement will be critical due to the low power requirements. In the scenario of a satellite digital audio radio system where an external satellite antenna is required, no existing FM modulation scheme is suitable for all existing arrangements of automobile FM receivers unless additional cabling is provided.